A steering apparatus for a vehicle is configured as illustrated in FIG. 12. Rotation of a steering wheel 1 is transmitted to an input shaft 3 of a steering gear unit 2, a pair of left and right tie rods 4 and 4 are pushed and pulled along with the rotation of the input shaft 3, and a steering angle is applied to front wheels. The steering wheel 1 is supported and fixed to a rear end portion of the steering shaft 5, and the steering shaft 5 is supported by a cylindrical steering column 6 so as to freely rotate in a state where the steering shaft 5 penetrates the steering column 6 in an axial direction. In addition, a front end portion of the steering shaft 5 is connected to a rear end portion of an intermediate shaft 8 through a universal joint 7, and a front end portion of the intermediate shaft 8 is connected to the input shaft 3 through another universal joint 9.
In the above-described steering apparatus, in the related art, it has been considered to provide a tilt mechanism for adjusting an up-down position of the steering wheel 1 or a telescopic mechanism for adjusting a front-rear position of the steering wheel 1 according to a physique and a driving posture of a driver (for example, refer to Patent Document 1). In the structure illustrated in the drawing, in order to configure a tilt mechanism, an upper front end portion of a housing 10 fixed to a front end portion of the steering column 6 is supported so as to be pivotally displaced with respect to a vehicle body 11 using a tilt shaft 12 disposed in a width direction (the width direction refers to a width direction of the vehicle body and matches a left-right direction; the same shall be applied throughout this specification and claims). In addition, a displacement bracket 13 is provided on a lower surface in the middle of the steering column 6 in the axial direction, and a fixing bracket 14 is provided in a state where the displacement bracket 13 is held between opposite sides in the width direction. Tilt-adjusting long holes 15 which are long in an up-down direction are formed in the fixing bracket 14, and telescopic-adjusting long holes 16 which are long in the axial direction (front-rear direction) are formed in portions of the displacement bracket 13 which match portions of the tilt-adjusting long holes 15, respectively. An adjusting rod 17 is inserted in a state where it penetrates the tilt-adjusting long holes 15 and the telescopic-adjusting long holes 16 in the width direction. In addition, the steering shaft 5 and the steering column 6 are expandable according to the above-described configuration. In the above-described structure, the telescopic-adjusting long holes 16 are long in the front-rear direction. As a result, the front-rear position of the steering wheel 1 can be adjusted. By manipulating an adjusting lever (not illustrated) provided in a first end portion of the adjusting rod 17, a force with which the displacement bracket 13 is held between the opposite sides in the width direction by the fixing bracket 14 is adjusted such that the position of the steering wheel 1 can be adjusted.
A more specific structure of the steering apparatus including the position-adjusting device for a steering wheel will be described with reference to FIGS. 13 and 14.
In the steering column 6, a front portion of an outer column 18 disposed on the rear side and a rear portion of an inner column 19 disposed on the front side are slidably fitted such that the overall length of the steering column 6 is expandable. In the front portion of the outer column 18 which is formed, for example, by die-casting a light alloy, a slit 20 is provided such that the inner diameter of the front portion is elastically expandable. In addition, a pair of left and right held plate portions 21 and 21 are provided in portions where the slit 20 is held between opposite sides in the left-right direction, and the displacement bracket 13 is formed of the held plate portion 21 and 21. In addition, in the held plate portions 21 and 21, the telescopic-adjusting long holes 16 and 16 which are long in the front-rear direction are formed. In addition, a pair of left and right support plate portions 22 and 22 which are provided in the fixing bracket 14 are disposed in portions where the displacement bracket 13 is held between opposite sides in the left-right direction. In the support plate portions 22 and 22, the tilt-adjusting long holes 15 and 15, which are long in the up-down direction and have a partial arc shape centering on the tilt shaft 12 (refer to FIG. 12), are formed. The adjusting rod 17 is inserted into the tilt-adjusting long holes 15 and 15 and the telescopic-adjusting long holes 16 and 16 in the width direction.
Further, the adjusting lever 23 is provided in a first end portion of the adjusting rod 17 in the axial direction. A nut 24 is provided in a second end portion of the adjusting rod 17 in the axial direction. A thrust bearing 25 and a cam device 28 including a driving cam 26 and a driven cam 27 are provided in a first end-side portion in the middle of the of the adjusting rod 17 in the axial direction. As a result, a lock mechanism is configured in which a gap between inner surfaces of the support plate portions 22 and 22 expands or contracts based on the pivoting of the adjusting lever 23. The adjusting rod 17 having the above-described configuration can move up and down along the tilt-adjusting long holes 15 and 15, but does not rotate along with the pivoting of the adjusting lever 23.
In order to adjust the position of the steering wheel 1, the adjusting lever 23 is pivoted in a predetermined direction (in general, downward) such that the driving cam 26 rotates in an unlocking direction. The dimension of the cam device 28 in the axial direction contracts, and a gap between the driven cam 27 and the nut 24 expands. As a result, a surface pressure of a contact portion between the inner surfaces of the support plate portions 22 and 22 and outer surfaces of the held plate portions 21 and 21 is reduced or lost. Concurrently, the inner diameter of a front end portion of the outer column 18 elastically expands, and a surface pressure of a contact portion between an inner peripheral surface of the front end portion of the outer column 18 and an outer peripheral surface of a rear end portion of the inner column 19 is reduced. In this state, the up-down position and the front-rear position of the steering wheel 1 can be adjusted in a range where the adjusting rod 17 is movable in the tilt-adjusting long holes 15 and 15 and the telescopic-adjusting long holes 16 and 16.
In order to maintain the steering wheel 1 in a desired position, the steering wheel 1 is moved to the desired position, and then the adjusting lever 23 is pivoted in a reverse direction (in general, upward). As a result, the driving cam 26 rotates in a locking direction which is a rotating direction for switching the steering wheel 1 to a locked state. The dimension of the cam device 28 in the axial direction expands, and the gap between the inner surfaces of the support plate portions 22 and 22 contracts. In this state, the surface pressure of the contact portion between the inner surfaces of the support plate portions 22 and 22 and the outer surfaces of the held plate portions 21 and 21 increases. Concurrently, the inner diameter of the front end portion of the outer column 18 elastically contracts, and the surface pressure of the contact portion between the inner peripheral surface of the front end portion of the outer column 18 and the outer peripheral surface of the rear end portion of the inner column 19 increases. As a result, the steering wheel 1 can be maintained at the adjusted position.
However, in the position-adjusting device for a steering wheel having the structure of the related art with the above-described configuration, in the state (unlocked state) where the position of the steering wheel 1 can be adjusted and in the state (locked state) where the adjusted position can be maintained, up-down-direction clearances 29a and 29b exaggeratedly illustrated in FIG. 14 are present between an outer peripheral surface of the adjusting rod 17 and inner surfaces (upper and lower surfaces) of the telescopic-adjusting long holes 16 and 16. In addition, although not illustrated in the drawing, front-rear-direction clearances are present between the outer peripheral surface of the adjusting rod 17 and inner surfaces (front and rear surfaces) of the tilt-adjusting long holes 15. In a case where the up-down-direction clearance 29a and 29b and the front-rear-direction clearances are present as above, the front-rear position and the up-down position of the steering wheel 1 can be smoothly adjusted.
However, in the locked state, the outer column 18 may substantially be displaced in the front-rear direction and the up-down direction by the up-down-direction clearances 29a and 29b or the front-rear-direction clearances. Therefore, the feeling of support rigidity of the steering wheel 1 deteriorates, and a driver may feel discomfort.